tests: fix internet/test-dns.js

internet/test-dns.js assumes that ::1 always resolves to "localhost" on
all platforms. This is not what happens in reality. Some platforms
resolve it to "ip6-localhost" too. There doesn't seem to be any consensus
on what's the right thing to do. However, most sane platforms will use
either one of these two values.

Reviewed-by: Trevor Norris <trev.norris@gmail.com>